Tennessee on Thursday imposed restrictions on the use of dicamba, becoming the fourth state to take action as problems spread over damage the weedkiller causes to crops not genetically modified to withstand it. Missouri on Thursday also announced
restrictions, partially rolling back an emergency ban announced last week.

Dicamba is sprayed by farmers on crops genetically modified to resist it but it has drifted, damaging vulnerable soybeans, cotton and other crops across the southern United States. Farmers have fought with neighbors over lost crops and brought lawsuits against
dicamba producers.

Arkansas banned its use last week and Missouri, which initially halted dicamba spraying on July 7, has joined Tennessee with tight restrictions on when and in what weather spraying can be done. Kansas is investigating complaints.

Monsanto, which said it has spent years working to make dicamba stickier and limit drift when it is sprayed, is campaigning to overturn the bans. It blames early-adoption headaches similar to wind drift and cross-contaminated farm equipment problems the
company faced when it launched its popular Roundup Ready glyphosate-resistant crops two decades ago.

The company, together with BASF SE and DuPont , which also produce dicamba-based weed killers, has agreed to additional safeguards for product use, Missouri Director of Agriculture Chris Chinn said in a statement.